1. Field of the Invention
The present invention relates to a plasma processing method and a plasma processing apparatus, and more particularly to a plasma processing method and a plasma processing apparatus for use in production processes for a semiconductor device, in particular, in an etching process.
2. Description of the Related Art
At present, in a production process of a semiconductor device, plasma etching and reactive ion etching (RIE), which use a plasma of a reactive gas, are widely used in an etching process to form a fine wiring pattern in the submicron line width region.
FIG. 4 is a schematic sectional side view of a conventional reactive ion etching apparatus. Referring to FIG. 4, high-frequency electrodes 3 and 4 opposite to each other are disposed in a processing container 7. A coupling condenser 8 is inserted between the electrodes 3 and 4 and connected to a high-frequency power supply 9 which supplies high-frequency electric power. A reactive gas inlet 5 and a reactive outlet 6 for introducing and exhausting reactive gas therethrough respectively are mounted in the processing container 7. A substrate 1 to be processed is laid on the high-frequency electrode 3, and furthermore, what is called a focus ring 2, which is a cylindrical insulator, is placed to surround the substrate 1.
The focus ring 2 functions to enhance the uniformity of progress of the etching reaction on the surface of the substrate 1. In general, the progress of the etching reaction is slower at the center portion of the substrate 1 than at the peripheral portion thereof. This is because etching reaction seeds at the center portion of the substrate 1 are depleted due to the etching reaction and this phenomenon is called the internal loading effect. The focus ring 2 functions to decrease the progress and speed of the etching reaction at the peripheral portion of the substrate 1, thereby achieving an excellent etching uniformity on the substrate 1.
It is thought that the etching speed is lowered at the peripheral portion of the substrate 1 by the focus ring 2 since the solid angle of incidence of the reaction ions onto the substrate 1 is restricted by the focus ring 2 as the reaction ions are incident nearer the peripheral portion of the substrate 2, than the center or by obstruction of the supply of neutral radical molecules contributing to the reaction. This reveals that the higher the focus ring 2 is, the lower the reactivity at the peripheral portion of the substrate I becomes. Therefore, the height of the focus ring 2 is an important parameter for obtaining excellent etching characteristics.
The conventional plasma processing apparatus is composed as described above and maintains a predetermined pressure in the processing container 7 by introducing a reactive gas, for example, CF.sub.4, CHF.sub.3, Cl.sub.2 or HCl, into the processing container 7 through the gas inlet 5 and simultaneously exhausting the gas in the processing container 7 through the outlet 6. By applying high-frequency voltage from the high-frequency power supply 9 between the high-frequency electrodes 3 and 4 in this state, a plasma in the reactive gas is generated between the high-frequency electrodes 3 and 4. At this time, the high-frequency electrode 3 on which the substrate 1 is laid is biased with a negative potential. Therefore, a region, called a sheath, having a strong electric field is generated between the plasma region and the high-frequency electrode 3. The speed of the reactive gas generated in the plasma is increased by the electric field in the sheath and the reactive gas is incident on the high-frequency electrode 3 and the substrate 1 laid on the high-frequency electrode 3. As a result, a thin film of, for example, polysilicon, previously formed on the substrate 1, is etched by the reaction of the incident ions.
Since the height of the focus ring 2 is an important parameter for controlling the uniformity of etching in the above-described plasma processing apparatus, it is necessary to finely adjust the height in accordance with process conditions such as the kind of film to be etched, the reactive gas to be used and the amount of high-frequency electric power. Furthermore, the recent high density integration of semiconductor devices requires uniform etching of a laminated film formed by laminating two different thin films (for example, a tungsten silicide/polysilicon laminated film or an aluminum alloy/titanium nitride laminated film).
However, since the focus ring 2 in the conventional plasma etching apparatus is fixed to the high-frequency electric supply 3 and the height thereof is constant, it is difficult to simultaneously obtain excellent etching characteristics of various kinds of thin films by using a focus ring 2 having a single height. Therefore, it is difficult to uniformly etch a laminated film with a single plasma processing apparatus.